Joseph Harris (February 1704 – 1764) was a British blacksmith, astronomer, navigator, economist, natural philosopher, government adviser and King's Assay Master at the Royal Mint.

Theophilus Jones, in A History of the County of Brecknock (1805), says that Joseph Harris, married one of the daughters, and heiress, of Thomas Jones, of Tredustan, and that "little has been recorded beyond the information derived from his monument in the church".

As far as biographies of Joseph Harris are concerned, things remain much the same now as they were in 1805, when Theophilus Jones was writing. The Harris family history of three brothers, all highly successful in entirely unrelated vocations, has tended to concentrate on the youngest of the three, Howell Harris, known as the "Apostle of Wales".

Joseph was baptised on 16 February 1703 in the church of Saint Gwendolen, Talgarth, on the slopes of the Black Mountains in the Welsh county of Brecknock, now part of Powys. His baptismal record falls between the beginning of January and the end of March, a period that until 1752 was in flux between the Julian and the Gregorian calendars, and with those three months considered in the Old Style as being part of the year that had just passed and in the New Style part of the year ahead; before 1752 this was expressed in the form of a fraction, the OS year uppermost and the NS year below. But it seems likely that the person who made the entry was confused, reversing the year dates; record keeping in Saint Gwendolen's had after all started only eight years earlier. It was at a later date that the incorrect OS year in that and similar entries was scored through, as well as recording a name change from Powell to Harries. Joseph was the first-born of Howell Powell, a joiner, and Susanna Powell, both of the same surname before, as well as after, their union, but how closely they were related, if at all, is not known. Their marriage is recorded in the parish register of Saint Gwendolen on 5 September 1702 and they lived in a small cluster of houses, the hamlet of Trefeca, (but then written Trevecka which sounds the same) about a mile south of, and in the parish of, Talgarth in the valley of the Breconshire Afon Llynfi, a tributary of the Welsh River Wye. Certainly by the time of the September 1704 baptism of the next child, daughter Anne, the family name of all its members had changed to Harries, an English name; nonetheless, all family members were bilingual in Welsh and English. Three further children were born in the next eleven years, of whom Thomas (bapt. June 1707) and Howell (bapt. February 1715 NS) survived beyond infancy to old age, while both Anne and an earlier Thomas (bapt. January 1706 NS) died soon after birth.

A similar, and related, confusion attends the record of Joseph's death on 26 September 1764. Both the memorial in Saint Gwendolen's and the record in Saint Peter ad Vincula in the Tower of London, in whose crypt he is buried, record him as being sixty-two years of age, which means he would have had to have been born before 26 September 1702; but in those days of high infant mortality it was thought essential to baptise a baby as soon as possible after birth to ensure his or her acceptance into Heaven, rather than Purgatory, should he or she succumb. A gap of five and a half months would have been negligent. The explanation for this discrepancy may well be that the sole source of the information was Joseph's only surviving offspring, Anna-Maria Harris, and the Harris family had in the past been vague about birthdays.

For Joseph's life in Trefeca before he moved to London, aged 21, the authority, apart from the church records and some reminiscences in his letters home from London, is the sometimes unreliable work of Theophilus Jones's History, which found little to say of him, as the quotation above shows. But we are told that he was apprenticed to his uncle Thomas Powell, a blacksmith, and that he met and fell in love with Anne Jones, one of three daughters of an eminent Brecknock family, whom he courted respectfully for at least 12 years and then married soon after he was appointed to the Royal Mint in 1736. From the fact that, despite the difference in their social position, Anne's father, Thomas Jones II, High Sheriff of Brecknock for 1722, recommended that she treat Joseph's attentions with respect, we may guess that his brilliance was well known locally. It may be that father and son Thomas Jones I and II had, as was common in Wales, thrown their library open to a gifted but poor village boy, thus explaining the description of Joseph as 'self-taught'. By the time of Joseph's arrival in London the family name had firmly become Harris. A surprising aspect of the failure of Theophilus Jones to find any information about Joseph is that Joseph's only surviving child, Anna-Maria, heiress to both Joseph and his wealthy middle brother, Thomas, living, like Theophilus, in the Brecon area, and by then married to Samuel Hughes, himself High Sheriff of Brecon in 1790, was one of the subscribers to Theophilus's work.

In the last weeks of 1724 Joseph moved to London with letters of introduction from Brecknock MP Roger Jones. Within a few days of Joseph's arrival in London he met the Governor of New England at Roger Jones's home, and Edmond Halley was showing him 'a quadrant worth at least £300', so it may not be far from the truth to assume that the introductions included one to the then Astronomer Royal. Joseph's letter home is the first in a collection of more than 3300 documents made by Howell, Joseph's youngest brother, now available in digest form in Boyd Stanley Schlenther and Eryn Mant White's Calendar of the Trevecka Letters (2003). The manuscripts themselves now lie in the Llyfrgell Genedlaethol Cymru/National Library of Wales, Aberystwyth. They are in the trusteeship of the Calvinist Methodist Church of Wales, who have not permitted transcriptions of the manuscript correspondence to be published.

From instructions to his family on how to address replies Joseph seems to have moved in with John Senex (1678-1740), notable chart- and map-maker. He then writes about how kind his 'Master' is and how he has given him 'German radish' seeds which he sends on to his family in Trefeca to try out; he was perhaps apprenticed to, but certainly working with, Senex. They co-operated to produce at least two star-maps, Stellarum Fixarum Hemisphaerium Australe and Boreale; in the plane of the equator; Joseph's name is writ large in the headline text, though the copyright remained in the hands of Senex, as after his death his wife sold it. A copy of Joseph's chart was in the library of Mme. Emilie du Chatelet, mistress and colleague of Voltaire, which may be the one now in the Bibliothèque Nationale de France and perhaps seized from her son's library when he was beheaded during the French Revolution. Although the pair of star maps in the plane of the equator are well represented in astronomy museums, there is also a further pair in the plane of the ecliptic. It is likely that production of these charts was related to the premature, much contested and hotly resented publication by Halley and Newton of Flamsteed's long delayed observations of the stars. In the Australe chart Joseph commemorates Polish astronomer Hevelius and King Jan III Sobieski's defeat of the invading Ottoman Turks in the 1683 Battle of Vienna, for the constellation Scutum is named Scutum Sobiescanum and illustrated with a glowing crucifix and the initials INRI. It is not easy to date the first publication of these charts, partly because the date 1690 too is large in the title and the facile tendency has been to take that as the publication date; but 1690 is before Joseph was born and during the childhood of Senex. The most likely period for its creation is when Joseph was working for John Senex, from January 1725 until he left on a voyage to Vera Cruz in June of that same year. When he returned from Vera Cruz in April 1728 he immediately started work on self-publishing his Treatise of Navigation and producing for Thomas Wright, instrument maker, his Description and Use of the Globe; and the Orrery. But it is an area that calls for more research. Wolfgang Steinicke in 'William Herschel, Flamsteed Numbers and Harris's Star Maps' says that these star-maps were still being relied on by William Herschel towards the end of the century.